The present invention is directed to high-coordination transition metal complexes, i.e., those of coordination number seven and above, and the use thereof in the room temperature/atmospheric pressure formation of carbon-carbon bonds via reductive coupling of linear carbon-containing ligands, and methods for the isolation and recovery of the newly formed C.sub.2 containing species.
The use of transition metals to catalyze the formation of new C--C bonds is an important part of industrial processes which use CO as a feedstock for products with more than one carbon atom. Commonly invoked mechanisms for metal catalyzed C--C bond making include carbonyl insertion (hydroformylation and methanol carbonylation) (see, Heck et al., J. Am. Chem. Soc., 1961, 83, 4023; and Calderazzo, Angew. Chem. Int. Ed. Engl., 1979, 17, 255), and polymerization of surface methylene (derived from CO and H.sub.2) on metal surfaces to give linear hydrocarbons in Fischer-Tropsch synthesis (see, Fisher et al., Brennst. Chem., 1926, 7, 97; Chem. Ber., 1926, 59, 830; and Brady et al., J. Am. Chem. Soc., 1980, 102, 6181; ibid, 1981, 103, 1287).
Other processes which effect C--C coupling include; (1) reductive elimination, Collman, et al., Principles and Applications of Organotransition Metal Chemistry, University Science Books, Mill Valley, CA, 1980, pp 234-245; (2) nucleophilic attack of carbanions at carbonyl, E. O. Fischer, Adv. Organomet. Chem., 1976, 14, 1, or olefin, R. A. Holton, J. Am. Chem. Soc., 1977, 99, 8083; (3) alkyl migration to carbonyl or carbene ligands; T. C. Flood, "Topics in Inorganic and Organometallic Stereochemistry", Eliel, et al., Wiley, New York, 1981, Vol. 12; Wojcicki, A. Adv. Organomet. Chem., 1973, 11, 87, Calderazzo, F. Angew Chem., Int. Ed. Engl., 1977, 16, 299; Threlkel, et al., J. Am. Chem. Soc., 1981, 103, 2650; Hayes, et al., ibid, 1981, 103, 4648; (4) coupling of alkynes, J. P. Collman, Acc. Chem. Res., 1968, 1, 136; McAllister, et al., J. Am. Chem. Soc., 1977, 99, 1666, nitriles Cotton, et al., J. Am. Chem. Soc., 1979, 101, 5094; de Boer, et al., J. Am. Chem. Soc., 1979, 153, 53, P. T. Wolczanski, Ph.D. Thesis, California Institute of Technology, Pasadena, CA, 1981; isonitriles, Giandomenico, et al., J. Am. Chem. Soc., 1982, 104, 1263; olefins, McDermit, et al., J. Am. Chem. Soc., 1976, 98, 6529; Erker, et al., ibid, 1979, 101, 5451, and/or aldehydes, Manriquez, et al., J. Am. Chem. Soc., 1978, 100, 2716, normally affording metallacyclic products; (5) addition of alkynes, McKinney, et al., J. Am. Chem. Soc., 1981, 103, 5584, olefins, Tebbe, et al., J. Am. Chem. Soc., 1978, 100, 3611; R. F., Schrock, J. Am. Chem. Soc., 1980, 102, 3272, to metal carbenes, yielding four-membered metallacycles; (6) bimolecular carbene-carbene coupling to olefins, Fisher, et al., Chem. Ber., 1974, 107, 3326; Schrock, et al., J. Am. Chem. Soc., 1978, 100, 2389; Casey, et al., J. Chem. Soc., Chem. Commun., 1975, 985, Ott, et al., J. Am. Chem. Soc., 1981, 103, 5922, and the less extensively documented processes (7) olefin insertion into metal-alkyl bonds; P. L. Watson, J. Am. Chem. Soc., 1982, 104, 337 and references therein; (8) carbene-carbonyl coupling to afford coordinated ketenes, Herrmann, et al., Angew. Chem. Int. Ed. Engl., 1978, 17, 525; Redhouse, et al., ibid, 1976, 15, 615; Herrman, et al., J. Am. Chem. Soc., 1979, 101, 3133; Wolczanski, et at., Acc. Chem. Res., 1980, 13, 121. D. H. Berry et al., J. Am. Chem. Soc., 1982, 104, 4712 reported a new type of carbon-carbon bond-forming reaction: the direct coupling of two carbonyl ligands of a binuclear transition-metal complex.
Compounds of the group 6 transition metals of the general formula [M(CNR).sub.7 ].sup.2+, [M(CNR).sub.6 X].sup.+ (R=alkyl, X=Cl, Br, I, CN, SnCl.sub.3 ; R=aryl, X=I), and M(CNR).sub.5 X.sub.2 comprise a well studied class; Giandomenico, et al., Organometallics, 1982, I, 142; Bonati, et al., Inorg. Chem., 1970, 9, 2642; Lewis, et al., Inorg. Chem., 1972, 11, 621; Novotny, et al., J. Chem. Soc., Chem. Commun., 1973, 202; Lewis, et al., J. Am. Chem. Soc., 1975, 97, 2697; Lam, et al., Inorg. Chem., 1978, 17, 2127; Brant, et al., J. Am. Chem. Soc., 1970, 101, 6588; Girolami, et al., J. Organomet. Chem., 1979, 182, C43; LaRue, et al., Inorg Chem., 1980, 19, 315; Mialki, et al., J. Am. Chem. Soc., 1980, 102, 1095; Szalda, et al., Inorg. Chem., 1981, 20, 3851. These complexs have close interligand contacts which could give rise to ligand migration or coupling reactions. Reductive coupling of two isocyanide ligands was found to occur in the reaction of [Mo(CN--t--C.sub.4 H.sub.9).sub.6 I].sup.+ with zinc. Lam, et al., J. Am. Chem. Soc., 1977, 99, 617. In particular, a brilliant red crystalline material was obtained, the nature of which was revealed by X-ray crystallography. The complex turned out to be [Mo(CN--t--C.sub.4 H.sub.9).sub.4 (CHN--t--C.sub.4 H.sub.9).sub.2 I]I, containing what is formally (N,N'-di-tert-butyldiamino)acetylene coordinated to molybdenum.
The Lam et al. chemistry was subsequently extended to the complexes [Mo(CN--t--C.sub.4 H.sub.9).sub.6 X].sup.+, wherein X=Cl and Br (Lam, C. T., Ph.D. Dissertation, Columbia University, New York, 1977). These gave the same type of product although the chloride and bromide complexes were obtained in lower yields and isolated as their tetrahalozincate(II) salts. The complex [Mo(CN--t--C.sub.4 H.sub.9).sub.6 I].sup.+ could be recovered from [Mo(CN--t--C.sub.4 H.sub.9).sub.4 (CNH--t--C.sub.4 H.sub.9).sub.2 I].sup.+ photochemically in the presence of free tert-butyl isocyanide. Corfield, et al., Inorg. Chem., 1981, 20, 922. No organic products were isolated, however.
An attempt to couple reductively tert-butyl isocyanide ligands in [Mo(CN--t--C.sub.4 H.sub.9).sub.7 ].sup.2+ gave rise to [Mo(CN--t--C.sub.4 H.sub.9).sub.4 (CNH--t--C.sub.4 H.sub.9).sub.2 (CN)].sup.+, in which both reductive coupling, (Lam, et al., J. Am. Chem. Soc., 1977, 99, 617,) and dealkylation of the tert-butyl isocyanide ligands occurred. (Dewan, et al., Inorg. Chem., 1981, 20, 4069.)
Giandomenico et al., in J. Am. Chem. Soc., 1982, 104, 1263-1271 describe the synthesis of a variety of seven-coordinated molybdenum(II) and tungsten(II) complexes containing linear ligands, especially alkyl isocyanides. These complexes, when subjected to reductive coupling conditions, permit the coupling of two of the isocyanide ligands, with the formation of a C.tbd.C bond. Recovery of the acetylene species by oxidation to the corresponding N,N-dialkyl oxamide was also reported.
Hoffmann et al., in J. Am. Chem. Soc., 1983, 105, 146-147, describe a "Theoretical Prescription for Reductive Coupling of CO or CNR Ligands" via transition metal complexes. It should be noted that the authors specifically state that the concept espoused is theoretical. The penultimate paragraph (p 147) reads as follows, "We look forward to experimental realization of this new reaction type."
However, Farr et al., in Organometallics, 1985, 4, 139-142, describe the synthesis and reactions of seven-coordinate technetium and rhenium complexes containing linear alkyl isocyanide ligands, and state that "attempts to couple the coordinated alkyl isocyanide ligands in the seven-coordinate technetium(III) and rhenium(III) complexes to produce coordinated (RNHC.tbd.CNHR) species, by analogy to known Mo(II) and W(II) chemistry, yielded only reductive elimination to form (M(CNR).sub.6).sup.+ cations." That is, by following the chemistry described in Giandomenico et al., supra, Farr et al. were unable to achieve reductive coupling. Failure to achieve reductive coupling of carbon monoxide using the techniques set forth by Hoffmann et al., supra, was also reported recently by Templeton et al., Inorg. Chem., 1985, 24, 2224-2230.
The present invention is directed to complexes and methods which achieve such a reductive coupling between linear carbon-containing ligands, particularly, carbon monoxide.